Objective To explore the influence of alexithymia on self-injury addiction of non-suicidal self-injury （NSSI） adolescents and the mediating role of internal emotional regulation in it， so as to provide reference for reducing self-injury addiction of NSSI teenagers. Methods A total of 123 adolescents diagnosed as NSSI in psychiatric outpatient department and inpatient department of the First Affiliated Hospital of Chongqing Medical University from December 2021 to August 2022 were recruited. The subscales of function and addiction of Ottawa Self-injury Inventory （OSI） and 20-Item Toronto Alexithymia Scale （TAS-20） were applied to investigate the cause of NSSI， self-injury addiction， and alexithymia. Pearson correlation analysis was used to analyze the correlation among the three. The mediating effect of internal emotion regulation between alexithymia and self-injury addiction was analyzed and tested using the Process plug-in and Bootstrap method. Results The total score of TAS-20 in 123 NSSI adolescents was （68.70±11.17）， the score of the functional subscale was （19.32±6.02）， the social influence was （15.29±6.24）， the external emotional regulation was （10.04±2.96）， the stimulation seeking was （6.30±3.21）， and the score of the addiction subscale was （20.26±8.16）. There was a statistically significant difference in the total TAS-20 scores among NSSI adolescents f different genders and whether they were only children （t=-2.64， -2.84； P ＜ 0.01）. The comparison of addiction subscale scores among NSSI adolescents with different parental marital status showed statistically significant differences （t=-2.03， P ＜ 0.05）. The score of TAS-20 was positively correlated with internal emotion regulation， social influence， external emotion regulation， stimulus-seeking dimension scores and addiction subscale score （r=0.24-0.58， P ＜ 0.01）. The internal emotional regulation of NSSI adolescents has a significant mediating effect between alexithymia and self-injury addiction， accounting for 46.34% of the total effect. Conclusions NSSI adolescent self-injury addiction may be related to internal emotional regulation and alexithymia， and internal emotional regulation plays a partial mediating role between alexithymia and self-injury addiction.